The present invention concerns an improved process for the preparation of 2-trifluoromethyl-5-(1-alkylthio)alkylpyridines from substituted enamines.
2-Trifluoromethyl-5-(1-alkylthio)alkylpyridines are useful intermediates for the preparation of certain new insecticides; see, for example, U.S. Pat. Nos. 7,678,920 and 7,687,634. U.S. Pat. Nos. 7,541,469 and 7,709,650 describe, inter alia, the condensation of a 4-alkoxy-1,1,1-trifluorobut-3-en-2-one with an enamine and the subsequent cyclization in the presence of ammonia or a reagent capable of generating ammonia. U.S. Patent Publication 2010-0004457 describes, inter alia, the condensation of a 4-chloro-4-alkoxy-1,1,1-trifluoro-2-butanone with an enamine in the presence of a tertiary amine base to provide a dienamine intermediate and its subsequent cyclization in the presence of ammonia or a reagent capable of generating ammonia. It would be desirable to have a process starting with 4-alkoxy-1,1,1-trifluorobut-3-en-2-one in which the condensation and cyclization reactions could be performed in the same convenient solvent and the unit operations could be reduced without decreasing overall reaction yield.